Have you ever heard a story that so profoundly affected you that it changed your entire point of view? I'm sure you have. There are all sorts of tall tales of investing: of fortunes won and lost, of Rule Breakers and Rule Makers, of small-cap skyrockets, and of deeply hidden values. Of all the stories I know from my brief investing career, the one that inspires me most features Benjamin Graham, founder of value investing and mentor to Berkshire Hathaway's Warren Buffett.

Graham emigrated from England with his family when he was barely a year old. He grew up in Manhattan and Brooklyn and went on to Columbia University, where he graduated in 1914. Though he had an opportunity with the family business, Graham instead opted for a career as a Wall Street analyst. By 1920, he was a partner at a major securities firm. Six years later, he formed the Benjamin Graham Joint Account, an investment fund he ran with partner Jerome Newman. But hard times would follow. From 1929 to 1932, the Joint Account declined by a breathtaking 70%.

That alone should have been enough, but the bad news kept compounding. It turns out that Graham had used substantial margin in making his selections. So when the stock market crashed, the massive debt he had piled up to buy stocks suddenly came due. And that borrowing nearly ruined him. Yet Graham persevered by selling personal assets and taking out loans with friends and family. Over the next 30 years, he and Newman would deliver 17% annualized returns to investors in the Joint Account. That's a remarkable record by any measure, and well north of the stock market's historical average return of 11% annually.

Graham never recounts this story in his landmark work, The Intelligent Investor. But the lessons he learned over 30 years of making money for others spring forth from every page. Here are two that continue to serve me well in my investing.

Lesson No. 1: Buying stocks makes you an owner
My favorite part of The Intelligent Investor comes toward the end, in the section that covers shareholder rights and responsibilities. Graham exhorts common stockholders to think of themselves as owners who have a right to answers. He writes: "Shareholders are justified in raising questions as to the competence of the management when the results (1) are unsatisfactory in themselves, (2) are poorer than those obtained by other companies that appear similarly situated, and (3) have resulted in an unsatisfactory market price of long duration."

In other words: If your investment is underperforming, you have every right to demand better. On more than one occasion, Graham did exactly that. Consider this tidbit from another wonderful investing work, John Train's Money Masters of Our Time: While combing through Interstate Commerce Commission filings in the mid-1920s, Graham found that Northern Pipeline had $95 per share in assets. The stock, however, was selling for $65 per share and yielding 9% at that price. Graham jumped at the opportunity. At the 1928 annual meeting, he garnered 38% of the proxies and was named to the company's board of directors. In that position, he would help persuade Northern Pipeline to pay out a huge $50 distribution to shareholders, clinching his original valuation thesis.

Graham thought stockholders were king. He rightly considered management as nothing more than a steward of the owners' money. Management was to invest intelligently and create market-trouncing returns or, in lieu of that, earn enough to pay a steady, growing dividend. He also expected a high degree of competence and ethical behavior from the managers of businesses in which he invested. He'd never stand to be a victim of corporate shenanigans, such as the rotten deal handed to Saucony (NASDAQ:SCNYA) (NASDAQ:SCNYB) shareholders or the recent flap at Quality Systems (NASDAQ:QSII). He'd have taken action, as an owner should. It is because of Graham's teachings that today I take proxy season as seriously as I take any national election. You should, too.

Lesson No. 2: Always buy with a margin of safety
Graham was perhaps the first stock analyst to understand this fundamental truth about investing: Price is everything. Indeed, buying shares of a great company means nothing if you overpaid. And buying rubbish on the cheap will frequently leave you with only the unpleasant odor of a rotting portfolio.

Graham details just how to buy with a margin of safety, which he calls the "central concept" of investing. Put simply, the "margin of safety" is the difference between the intrinsic value and the price at which a stock trades. For example, a security worth $50 per share but trading at $25 per share enjoys a massive 100% margin of safety. Buying in that situation heavily stacks the odds in favor of the investor.

Conversely, a stock that trades close to or above its intrinsic value offers almost no margin of safety. And buying without a margin of safety, in Graham's book, is no better than mere speculation. Or worse, gambling. Consider the recent performance of oft-hyped stocks Altair Nanotechnologies (NASDAQ:ALTI), Baidu (NASDAQ:BIDU), and Human Genome Sciences (NASDAQ:HGSI) to see what I mean.

Finally, seeking a substantial margin of safety can light the path to outsized returns. It has certainly helped Philip Durell, lead analyst for Motley Fool Inside Value. Take his investment in Omnicare (NYSE:OCR), for example. When Philip recommended Omnicare in the November 2004 issue, the stock enjoyed a very healthy 28% margin of safety. Subscribers who followed his advice and invested are up more than 80% in less than a year.

The Foolish bottom line
I've read and re-read my copy of The Intelligent Investor. It is lined with yellow highlighter ink. Reading that book was one of the most important steps I took toward developing a lucid investment strategy. And I believe Buffett was right when he called it the "best book on investing ever written."

I treasure Graham's work because he took research seriously. His use of data is so crisp and compelling, he could have been a lawyer. Every page advances the argument that if you want to beat the market, you must buy stocks on sale. The Intelligent Investor offers the richest blueprint I've yet seen for how to do exactly that. Fortunately, Fool, we're prepared to give it to you for free.

Sign up for a one-year subscription to Inside Value, and you'll get the book and full access to a service that has outperformed the market since inception. We'll refund your money in full within 30 days if you're not completely satisfied. And you can cancel at any time without obligation. That's a margin of safety any Fool can appreciate.

This article was originally published on May 31, 2005. It has been updated.

Fool contributor Tim Beyers breaks the rules in his portfolio from time to time, but he still appreciates a good value as much as any Fool. Tim owns shares of Berkshire Hathaway, but no other companies mentioned in this article. To see the stocks in Tim's portfolio, check out his Fool profile . Quality Systems is a Motley Fool Stock Advisor recommendation. Saucony is a Motley Fool Hidden Gems recommendation. The Motley Fool has an ironcladdisclosure policy.